This proposal is for the continuation of earlier studies on the tissue distributions and toxicity of the x-ray contrast media. The proposed research to be carried out by a team of individuals experienced in this field falls into four major categories: 1) study of the chemical basis for contrast-tissue interactions, 2) the subcellular basis of reactions occurring with contrast media, 3) cellular or organ responses to contrast perfusion, 4) metabolic considerations. Chemical studies will involve both a continuing survey of contrast- protein interactions and a beginning effort at the design and development of new contrast media based on past experience. Subcellular reactions studied will include interactions with red blood cells and with liver cells. Organ response to contrast perfusion will include a continuing survey of both allergic and chemotoxic reactions involving principally the kidney and lungs. Under metabolic considerations, we plan to further examine the factors influencing the absorption and hepatic pharmacodynamics of the cholecystographic and cholangiographic media.